(a) Field of the invention:
The present invention relates to an attachment which houses an observation optical system and an illumination optical system, and which is removably mounted at the foremost end portion of an endoscope such as fiberscope, non-flexible endoscope or electronic scope.
(b) Description of the prior art:
Endoscopes, in general, are such that various diversified component parts such as fiber bundles for observation, fiber bundles for illumination, a forceps channel, an air-supply tube, a water-supply tube, etc. require to be incorporated in a narrow tube of a diameter of the order of 10 mm at the largest. Therefore, it is the present state of art that all the necessary component parts may not be accomodated in a narrow tube unless the fill-up degree of these component parts is elevated by, for example, forming the cross sectional shape of the illumination fiber bundles not necessarily in a circular shape but, instead, making them in various other different shapes such as oval or semi-circular cross sections, and by winding them around a tube which supports the observation optical system, or by dividing the illumination fiber bundle into a plurality of narrow fiber bundles having such different cross sectional shapes as mentioned above and passing them through narrow spaces existing between a number of component parts.
In case the abovesaid attachment is disposed at the foremost end portion of an endoscope as stated above and in case the focal distance or the direction of visual field is intended to be altered, it will be noted that, in the event that the illumination fiber bundle B has a circular end surface and is bifurcated at the forward end portion of the endoscope body F as shown in FIGS. 1 and 2, not only the optical system 2 for switching over to the side-viewing which is aligned with the observation optical system O provided within the endoscope body F, but also the illumination system which comprises two light-guide members 3, 3 both having a circular cross section and aligned with the illumination fiber bundles B, B, respectively, which jointly constitute the illumination optical system and which also comprises two illumination lenses 4, 4 provided, respectively, at the light-emitting ends of the respective light-guide members, has been constructed in the past in such a form as if the illumination optical system per se on the endoscope body F side is extended in its length, also within the attachment 1 which is removably mounted onto the endoscope body F.
As stated above, in the attachment of the conventional type mentioned above, there have been the problems bringing forth such an inconvenience as represented by an increase in the number of optical parts which, in turn, leads to an increase in the manufacturing cost, and not only that, but also the inconvenience that, when it is intended to provide an arrangement for a wide angle viewing, the outer diameter of the illumination lens becomes larger, and in case of, for example, side-viewing, the space per se of the region in which a lens is disposed is too narrow for the accomodation of an illumination lens and/or the observation lens, so that if, for example, the illumination lens is forcibly reduced in size for being accomodated in the predetermined space, this will lead to vignetting, by the illumination lens, of a part of the illumination light which is transmitted by the illumination fiber bundle, leading to an insufficient amount of light available in the peripheral regions of the visual field.